Diatom, a type of microalgae, is the main food for fishes, shellfish and shrimps, especially for their larvae, and creates primary productivity in ocean together with other plants. In terms of biological taxonomy, diatom resides in Bacillariophyta, and based on shell shape and pattern arrangement mode, diatoms can be classified into two classes: centric diatoms (Centrales), which are radially symmetrical and pennate diatoms (Pennales), which are bilaterally symmetrical. The former are paraphyletic to the latter. CN200310120738.3 discloses a diatom culture solution and a method for diatom culture by the culture solution. In closed culture, the culture solution need to be measured frequently and quantitatively supplemented. High-density monoculture of diatoms requires complex production process and high cost.
Existing microalgae culture methods can be classified in two types: close culture and open culture. In open culture microalgae cultivation is performed using an open bioreactor such as runway pond, round shallow pond culture device and other culture devices, and it is featured by low investment; currently, only a few algae, like spirulina, chlorella and dunaliella, have been produced in industrial production by the open cultivation technique, whereas continuous open diatom cultivation has not been done in large scale, because the difficulty in the maintenance of a selected species in open culture due to the invasion of other species and predators
Closed photo-bioreactors have been used for microalgae cultivation, such as air-lift culture device, stirring culture device and tube culture device; the closed culture can be used for producing high-value products (e.g. medicines or healthcare products) or used as a seed tank for open pond culture, where the high cost of closed production system is less important.